Double-side exposed semiconductor device

ABSTRACT

A double-side exposed semiconductor device includes an electric conductive first lead frame attached on top of a thermal conductive but electrical nonconductive second lead frame and a semiconductor chip flipped and attached on top of the first lead frame. The gate and source electrodes on top of the flipped chip form electrical connections with gate and source pins of the first lead frame respectively. The flipped chip and center portions of the first and second lead frames are then encapsulated with a molding compound, such that the heat sink formed at the center of the second lead frame and the drain electrode at bottom of the semiconductor chip are exposed on two opposite sides of the semiconductor device. Thus, heat dissipation performance of the semiconductor device is effectively improved without increasing the size of the semiconductor device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of a pending U.S. patentapplication entitled “DOUBLE-SIDE EXPOSED SEMICONDUCTOR DEVICE AND ITSMANUFACTURING METHOD” by Yuping Gong et al with application Ser. No.13/193,474, and filing date of Jul. 28, 2011 whose content is herebyincorporated by reference for all purposes.

TECHNICAL FIELD

This invention relates to a semiconductor device and its manufacturingmethods, specifically relates to a double-side exposed semiconductordevice for improvement of the thermal dissipation performance.

BACKGROUND TECHNOLOGY

In applications of semiconductor power devices, the device's size andheat dissipation are two important parameters. To improve thermalperformance, thinner semiconductor wafer is used and large area isexposed out of the package without increasing the size of the devices.Conventional semiconductor devices use the exposure of source or drainto improve heat dissipation.

FIG. 1 and FIG. 2 are cross-sectional and perspective views of anexisting semiconductor device, in which the gate 110 and source 120 of asemiconductor chip 100 are located at the top of the semiconductor chip100 and connect to pins 151, 152 respectively through solder balls 140.The drain 130 located at the bottom of the semiconductor chip 100 isdirectly exposed from the molding compound 160. The exposed area of thedrain 130 can be the whole bottom surface of molding compound 160, asshown in FIG. 2, or can be a part of bottom surface of molding compound160, as shown in FIG. 1. In this device, only the surface of drain 130is exposed for heat dissipation.

FIG. 3 is a cross-sectional schematic view of another existingsemiconductor device. In this device, drain 130 of a flipped chip 100 isconnected to a heat sink 170 that is exposed from the top surface of themolding compound 160. The gate and source of flipped chip 100 areconnected correspondingly to pins 191, 192 through solder balls 140. Thebottom of pins 191, 192 is exposed from the molding compound 160, whichimproves the thermal performance.

However, the process of manufacturing of the existing devices is verycomplicated.

SUMMARY OF THE INVENTION

A double-side exposed semiconductor device includes a bottom electrodeof a semiconductor chip and a heat sink of a lead frame expose on twoopposite sides of the device for improvement of the heat dissipationperformance.

An electrical conductive first lead frame, which includes a plurality ofpins, is attached on a top surface of a thermal conductive andelectrical non-conductive second lead frame that includes a heat sink.The bottom surface of the second lead frame is coated with Ni or Cu.

A semiconductor chip including top electrodes and bottom electrodes isflipped and attached on top of the first lead frame. As such, topelectrodes of the semiconductor chip are facing downward andelectrically connecting to corresponding pins of the first lead frame.

A molding compound is deposited to encapsulate the flipped chip and thecenter portions of the first and second lead frames such that the heatsink of the second lead frame and bottom electrode of the semiconductorchip are exposed on two opposite sides of the semiconductor device.

The first lead frame can be made from copper (Cu) or other electricalconductive materials. The second lead frame is made from alumina (Al₂O₃)or aluminum nitride (AlN) or other thermal conductive but electricalnonconductive materials. The first lead frame is connected to the secondlead frame using welding or epoxy bonding techniques.

In one embodiment, the bottom electrode of the semiconductor chipincludes drain electrode and the top electrodes include gate and sourceelectrodes. As such, the pins of the first lead frame include gate pinsand source pins. The heat sink of the second lead frame is positionedbeneath the connected positions of the gate electrode and the gate pinand the source electrode with the source pins.

In one embodiment, the semiconductor chips, each of which includesbottom drain electrode and top gate and top source electrodes, areformed in a semiconductor wafer. Solder balls are formed on the gate andsource electrodes and then are connected correspondingly to the gatepins and source pins of the first lead frame. The wafer is ground on itsback surface to a predetermined thickness. The individual semiconductorchips are then singulated from the wafer. A conductive layer is thenformed on the back surface of the thinned wafer, for example through theevaporation of Ti, Ag or Ni, which functions as the drain electrode andalso a protective layer of the semiconductor chip.

In one embodiment, the semiconductor chip also contains a chip moldingcompound that covers the top surface of the wafer and the solder balls.Top portions of the chip molding compound and solder balls are thenground to expose the top surface of the solder ball with the top surfaceof the solder ball and top surface of the chip molding compound beingco-planar. The individual semiconductor chips are then singulated fromthe wafer.

In one embodiment, the semiconductor chip also contains a chip moldingcompound that covers the top surface of the wafer and the solder ballswith top portions of solder balls protruded from the chip moldingcompound. The individual semiconductor chips are then singulated fromthe wafer.

In the double-side expose semiconductor device, the part of gate pinsand source pins of the first lead frame not covered by the moldingcompound are bended in a ladder shape with the ends of these pins beingon a same plane with the exposed drain of the flipped chip.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 and FIG. 2 are cross-sectional and perspective schematic diagramsof a conventional semiconductor device with the drain electrode of thesemiconductor chip exposed at a bottom of the semiconductor devicepackage.

FIG. 3 is cross-sectional schematic diagram of another conventionalsemiconductor device with the drain of the semiconductor chip connectedwith a heat sink and exposed at the top surface of semiconductor device.

FIG. 4 is a perspective schematic diagram of a first lead frame.

FIG. 5 is a perspective schematic diagram of a second lead frame.

FIG. 6 is a perspective schematic diagram of a connection structure offirst and second lead frames.

FIG. 7 to FIG. 10 are perspective schematic diagrams illustrating thesteps of forming a first structure of the semiconductor chip used in adouble-side exposed semiconductor device of the present invention.

FIG. 11 to FIG. 16 are perspective schematic diagrams illustrating thesteps of forming a second structure of the semiconductor chip used in adouble-side exposed semiconductor device of the present invention.

FIG. 17 to FIG. 21 are perspective schematic diagrams illustrating thesteps of forming a third structure of the semiconductor chip used in adouble-side exposed semiconductor device of the present invention.

FIG. 22-25 are perspective schematic diagrams showing the steps offorming a double-side exposed semiconductor device of the presentinvention.

DETAILED DESCRIPTION OF THE DRAWINGS

The specific embodiments of the double-side exposed semiconductor deviceand its manufacturing methods in the present invention will beillustrated with the attached drawings.

FIGS. 22-25 are perspective views showing the steps of forming adouble-side exposed semiconductor device of the present invention. Asshown in FIG. 22, a first lead frame 10 is attached on top of a secondlead frame 20. A semiconductor chip 30 is flipped and attached on top ofthe first lead frame 10 with the bottom electrode 33, i.e., a drainelectrode, of the semiconductor chip exposed at the top surface of thestructure. As shown in FIG. 23, a molding compound 40 is deposited toencapsulate the flip chip 30 and covers center portions of the first andsecond lead frames 10, 20. As shown in FIG. 24, the excess parts atedges of the first and second lead frames are removed and the parts ofthe pins 11 and 12 that are not covered by the molding compound 40 arebended upward toward the drain 33. As shown in FIGS. 24 and 25, the heatsink 21 formed in the second lead frame 20 and the drain 33 at thebottom of the semiconductor chip 30 are exposed from the moldingcompound 40 on two opposite sides of the semiconductor device.

FIG. 4 is a perspective view showing the first lead frame 10 including agate pin 11 and a source pin 12. The first lead frame 10 can be madefrom copper or other electrical conductive materials.

FIG. 5 is a perspective view showing the second lead frame 20 includinga heat sink 21 formed at the center of the second lead frame 20. Thelead frame 20 can be made from aluminum oxide (Al₂O₃), aluminum nitride(AlN) or other heat conductive but electrical nonconductive materialswith Nickel (Ni), or copper (Cu) coating only on back surface of thesecond lead frame 20.

As shown in FIG. 6, the first lead frame 10 is attached on top of thesecond lead frame 20 using welding or epoxy bonding method, such thatportions of gate pin 11 and source pin 12 at the center of the firstlead frame 10 are vertically aligned with the heat sink 21 at the centerof the second lead frame 20. The top surface of the second lead frame 20that is physically connected to the first lead frame 10 is not coatedwith Nickel or Copper to prevent short circuit.

The semiconductor chip 30 used in the double-side exposed semiconductordevice package described in FIGS. 22-25 can be one of the threedifferent structures as described below.

FIGS. 7-10 are perspective views showing the steps of making a firststructure of the semiconductor chip 30. Referring to FIG. 7,semiconductor chips are formed on a top surface of a semiconductor wafer34, each of which includes source 32 and gate 31 at the top of thesemiconductor chip and a drain 33 at the bottom of the semiconductorchip. Solder balls 351 and 352 are formed at gate 31 and source 32 ofsemiconductor chip 30 on top surface of the wafer 34, as shown in FIG.8. The wafer 34 is ground at its back surface to a predeterminedthickness as shown in FIG. 9. A conductive layer 36 is deposited on theback surface of thinned wafer 34, for example by evaporation of Ti, Agor Ni materials at the back surface of the thinned wafer during themetallization process, which is electrically connected to the drain 33at the bottom of the semiconductor chip and also functions a protectivelayer of the semiconductor chip 30 as shown in FIG. 10. Finally, thewafer 34 is cut to separate semiconductor chips 30 (not shown).

FIGS. 11-16 are perspective views illustrating the steps of making afan-in structure of the semiconductor chip 30. FIG. 11 and FIG. 12 areequivalent to FIG. 7 and FIG. 8, in which solder balls 351 and 352 areformed on top surface of semiconductor wafer 34 at gate 31 and source 32respectively of semiconductor chip 30. A molding compound 37 isdeposited to cover the top surface of wafer 34 and the solder balls351,352, as shown in FIG. 13. The molding compound 37 is then ground toexpose the solder balls 351, 352 with the exposed portions of the solderballs 351, 352 are also ground away, so that the top surface of solderballs 351,352 and the top surface of thinned molding compound 37 areco-planar, as shown in FIG. 14. The wafer 34 is then ground at its backsurface to reduce its thickness, as shown in FIG. 15. A conductive layer36 is deposited on the back surface of thinned wafer 34, for example byevaporation of Ti, Ag or Ni materials at the back surface of the thinnedwafer during the metallization process, which functions as a drainelectrode and also a protective layer of the semiconductor chip 30, asshown in FIG. 16. Finally, the wafer 34 is cut to separate semiconductorchips 30 (not shown).

FIGS. 17-21 are perspective views illustrating the steps of making afan-out structure of the semiconductor chip 30. FIG. 17 and FIG. 18 areequivalent to FIG. 7 and FIG. 8, in which solder balls 351 and 352 areformed on top surface of semiconductor wafer 34 at gate 31 and source 32respectively of semiconductor chip 30. A molding compound 38 isdeposited to cover the top surface of wafer 34 but not cover the wholesolder balls 351, 352, i.e., the top portions of the solder balls 351,352 are protruded from the molding compound 38 as shown in FIG. 19. Thewafer 34 is then ground at its back surface to reduce its thickness, asshown in FIG. 20. A conductive layer 36 is deposited on the back surfaceof thinned wafer 34, for example by evaporation of Ti, Ag or Nimaterials at the back surface of the thinned wafer during themetallization process, which functions as the drain electrode and also aprotective layer of the semiconductor chip 30 as shown in FIG. 21.Finally, the wafer 34 is cut to separate semiconductor chips 30 (notshown).

As shown in FIG. 22, semiconductor chip 30 of any structure typedepicted above in FIGS. 10, 16 and 21 is flipped and electricallyconnected to the first lead frame 10. The solder balls 351 and 352formed at the gate 31 and source 32 of the flip-chip 30 are electricallyconnected to the gate pin 11 and the source pin 12 respectively on thefirst lead frame 10. Drain 33 of the flip chip 30 is then exposed fromthe top surface of molding compound 40 (as shown in FIG. 23 and FIG.24).

As described above, as shown in FIG. 25, the back surface of the heatsink 21 of second lead frame 20 is exposed from the bottom surface ofmolding compound 40. The heat sink 21 is used to improve the heatdissipation of junctions between gate 31 of semiconductor chip 30 withgate pin 11 and between source 32 of semiconductor chip 30 with sourcepin 12. As shown in FIG. 24 and FIG. 25, the portions of the gate pin 11and source pin 12 that are exposed outside of the molding compound 40are bended in a ladder shape with the end of pins 11 and 12 being in thesame plane with the exposed drain 33, so that the semiconductor devicepackage can be connected with the external printed circuit board orother electronic devices through the gate pin 11, source pin 12 anddirectly to exposed drain 33.

The double-side exposed semiconductor device of the present inventionincludes the heat sink 21 and the drain 33 of the semiconductor chip 30exposing from the molding compound, thus the heat dissipationperformance of the semiconductor device can be improved effectivelywithout increasing the size of the device.

Although the contents of this invention have been described in detail inthe above said preferred embodiments, it should be recognized that theabove description shall not be considered as a limitation for thisinvention. After reading the above description by technical personnel inthis field, a number of modifications and replacements for thisinvention will be obvious. Therefore, the scope of protection for thisinvention shall be in accordance with the attached claims.

The invention claimed is:
 1. A double-side exposed semiconductor devicecomprising: an electrical conductive first lead frame including aplurality of pins; a thermal conductive and electrical nonconductivesecond lead frame including a heat sink, wherein the first lead frame isattached on a top surface of the second lead frame; a semiconductor chipincluding top electrodes and bottom electrodes, wherein thesemiconductor chip is flipped and attached on top surface of the firstlead frame with the top electrodes of the semiconductor chip electricalconnected to corresponding pins on the first lead frame; a moldingcompound encapsulating the flipped semiconductor chip and centerportions of the first and second lead frames wherein the heat sink ofthe second lead frame and the bottom electrodes of the semiconductorchip are exposed from the molding compound on two opposite sides of thesemiconductor device wherein the first lead frame is made from copper(Cu) or other electrical conductive material and the second lead frame(20) is made from alumina (Al₂O₃), aluminum nitride (AlN) or otherthermal conductive and electrical nonconductive material, with Ni or Cucoating only on a back surface of the second lead frame, and wherein thefirst lead frame is connected to non-coating surface of the second leadframe.
 2. The double-side exposed semiconductor device of claim 1,wherein the first lead frame is attached to the second lead frame usingwelding or epoxy bonding technique.
 3. A double-side exposedsemiconductor device comprising: an electrical conductive first leadframe including a plurality of pins; a thermal conductive and electricalnonconductive second lead frame including a heat sink, wherein the firstlead frame is attached on a top surface of the second lead frame; asemiconductor chip including top electrodes and bottom electrodes,wherein the semiconductor chip is flipped and attached on top surface ofthe first lead frame with the top electrodes of the semiconductor chipelectrical connected to corresponding pins on the first lead frame; amolding compound encapsulating the flipped semiconductor chip and centerportions of the first and second lead frames wherein the heat sink ofthe second lead frame and the bottom electrodes of the semiconductorchip are exposed from the molding compound on two opposite sides of thesemiconductor device wherein the bottom electrode of the semiconductorchip, which is exposed from the molding compound, includes a drainelectrode, and the top electrodes of the semiconductor chip include agate electrode and source electrode, and wherein of the plurality ofpins formed in the first lead frame includes a gate pin connecting tothe gate electrode and a source pin connecting to the source electrode,and wherein the heat sink on the second lead frame is positioned belowthe gate electrode and the source electrode.
 4. The double-side exposedsemiconductor device of claim 3 wherein the semiconductor chip is formedon top of a wafer with solder balls deposited on the gate electrode andsource electrode of the semiconductor chip and correspondingly connectedto the gate pin and the source pin of the first lead frame when thesemiconductor chip is attached on the first lead frame, and wherein thesemiconductor wafer is ground on its back surface to a predeterminedthickness and is then deposited on its back surface with a conductivelayer that functions as a drain electrode and a protective layer of thesemiconductor chip.
 5. The double-side exposed semiconductor device ofclaim 4, further comprising a chip molding compound covering the topsurface of the semiconductor wafer and encapsulating the solder balls,wherein top portions of the chip molding compound and solder balls areground such that a top surface of the solder balls are exposed from thechip molding compound and are co-planar with the top surface of the chipmolding compound.
 6. The double-side exposed semiconductor device ofclaim 4, further comprising a chip molding compound covering the topsurface of the semiconductor wafer and encapsulating the solder balls,such that top portion of the solder balls are protruded out of the topsurface of the chip molding compound.
 7. The double-side exposedsemiconductor device of claim 3, wherein portions of the gate pin andsource pin that are not covered by the molding compound are bended in aladder shape with ends of the gate and source pins being on a same planewith the exposed drain electrode of the flipped semiconductor chip.